1. Field of the Invention
Apparatuses and methods consistent with the present invention relates to a bent-shaped metallic waveguide having a tapered C-shaped aperture, and more particularly, to a bent-shaped metallic waveguide that can be manufactured in an integrated structure and realize a reinforced near field effect, a method of fabricating the waveguide, a light delivery module including the waveguide, and a heat assisted magnetic recording head having the waveguide.
2. Description of the Related Art
In the field of a magnetic recording head, much research has been conducted on high-density magnetic recording. A recording density of 100 Gbit/in2 has been achieved in horizontal magnetic recording, and a recording density of 100 Gbit/in2 or more may be possible in vertical magnetic recording. However, the magnetic recording technology still has a limitation in providing high recording density because of thermal instability which occurs during recording due to a super paramagnetic effect.
The thermal stability in a recoding medium is determined by the ratio of magnetic anisotropy energy to thermal energy. To increase the magnetic anisotropy energy, a magnetic recording medium must be formed of a material with a strong coercive force. When the magnetic recording medium is formed of a material with a strong coercive force, a correspondingly strong magnetic field is required for recording. However, since a small-sized recording head is used to increase the recording density, the magnetic field of a main pole is saturated at a predetermined level. Therefore, recording is impossible due to a limited strength of a generated magnetic field.
To solve this problem, a heat-assisted magnetic recording (HAMR) method has been developed. In the HAMR method, the coercive force of the corresponding position is temporarily decreased by heating a local portion of the recoding medium above the Curie temperature. When compared to a related art magnetic recording method, the HAMR method can further reduce the strength of a magnetic field required for recording. At this point, since data is recorded in a region heated above the Curie temperature, the recording density is determined by the width of the heated portion rather than the size of a pole generating a magnetic field. For example, when a heating unit is a laser diode, a data recording density is determined by the spot size of a laser light emitted from the laser diode.
Accordingly, the HAMR head requires a light delivery module for emitting laser light to the recording medium. The light delivery module delivers the light to a location near the main pole. In addition, the light delivery module provides a high light intensity while reducing a spot size of light focused on the recording medium. Such a light delivery module includes a light source, a waveguide, and a small aperture, and is integrated in a small space near the main pole. However, in order to significantly change a structure of a related art magnetic head, the location where the light delivery module can be disposed is limited. For example, a waveguide for delivering light from a light source to a small aperture must be vertically disposed on a main pole. In this case, a direction of the waveguide is different from a direction of the small aperture disposed near an end of the main pole by 90°. Therefore, an optical element for changing the light direction by 90° must be disposed between the waveguide and the small aperture. A mirror may be used as the optical element. However, it is technologically difficult to integrate the optical element having a bulky structure on the related art magnetic head with a very thin thickness.
Furthermore, it is desirable that the optical delivery module be fabricated through a batch process that is identical to a process for fabricating the related art magnetic head process. To realize this, a waveguide and a small aperture that can be fabricated through a planar process at a lower temperature equal to or less than 175° C. are necessary.
Meanwhile, the small aperture delivers the light transmitted through the waveguide to a recording layer of the recording medium. At this point, in order to realize a high recording density, the light delivered to the recording layer must have a small spot size and high intensity in order to heat the recording layer up to about the Curie temperature. Generally, the spot size is determined by a size of the small aperture. It can be expected that the smaller the size of the aperture, the higher the recording density. However, when the aperture is significantly smaller than a wavelength of incident light, power throughput of the aperture is significantly reduced. For example, when a circular aperture has a radius r that is equal to or less than 1% of a wavelength of incident light, the power throughput of the aperture is reduced by a rate of r4. That is, when the aperture is small-sized, high spatial resolution can be realized but the power throughput is too small. Therefore, there is a limitation in applying the small-sized aperture to a HAMR head.
Accordingly, in order to solve the low transmission problem, research on a near field optical probe continue and probes having a variety of small apertures have been proposed. However, a near field probe that has both high transmission and high resolution, and reliability and reproducibility that are appropriate for a HAMR head has not been yet developed.